Nervous System
The nervous system and the endocrine system together
integrate one communication function of the human body
The nervous ...
Central nervous system
• Structural and functional center of the entire nervous system
• Consists of the brain and spinal ...
Peripheral nervous system
• Consists of the nerve tissues that lie on the periphery or
regions outside the CNS
• Cranial n...
A-fferent division – consists of all
incoming sensory or afferent
pathways
E-fferent division – consists of all
outgoing...
Somatic nervous system – carry information to the
somatic effectors (skeletal muscles)
• Somatic motor division – efferent...
Autonomic nervous system – carry information to the
autonomic (visceral) effectors
• Sympathetic division – pathways that ...
Neurons consist of a cell body, one or more dendrites, and one axon
• Distal ends of dendrites of sensory neurons are call...
Classification of neurons – three distinct structural types of
neurons
• Multi-polar neurons – have only one axon but seve...
Classification of neurons – according to the direction in
which they conduct impulses
• A-fferent (sensory) neurons – tran...
Reflex arc – automatic signal conduction route to and
from the CNS
• Most common form of reflex arc is the three-
neuron a...
Neur/o-gli/o - al(Neuroglial)– pertaining to the support cells, glial cells, of nerves.
Five basic types:
• Astro-cytes – ...
Neur/o – al – (Neural) – Pertaining to nerves.
Nerves - bundles of peripheral nerve fibers (axons) held together by
severa...
Tracts – bundles of nerve fibers within the CNS
White matter – bundles of myelinated fibers
Gray matter – cell bodies a...
Mixed nerves – carry both sensory (afferent) and
motor (efferent) fibers
Sensory nerves – contain mostly afferent fibers...
Nerve impulse – wave of electrical energy that travels along the
plasma membrane of the nerve
Cell membrane potential – di...
Synapse – place where signals are
transmitted from one neuron,
called the pre-synaptic neuron, to
another neuron, called t...
Types of synapses
• Electrical synapse – where two cells are joined end-to-end by gap junctions; as a result, an
action po...
Neuro-transmitters – means by which neurons “talk” to
one another; more than 50 compounds are now
known to be neurotransmi...
•Excitation – occurs when a stimulus
triggers the opening of stimulus-gated
Na+ channels
•Inhibition – stimulus triggers t...
Action potential – an electrical signal that travels along the surface
of a neuron’s plasma membrane
• When an adequate st...
Absolute refractory period – very
brief period when a local area of an
axon’s membrane resists
restimulation
Conduction of the action potential
• The action potential never moves backward,
restimulating the region from which it jus...
Severe psychic depression occurs when a
deficit of norepinephrine, dopamine,
serotonin, and other amines exists in certain...
Cocaine – produces a temporary feeling
of well-being in cocaine abusers by blocking
the uptake of dopamine
Anesthetics –...
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
Nervous system
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Biology 120 Presentation - Chapter 12 - Nervous system

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Nervous system

  1. 1. Nervous System
  2. 2. The nervous system and the endocrine system together integrate one communication function of the human body The nervous system is subdivided in a variety of ways according to its structure, the direction of information flow, and the control of effectors
  3. 3. Central nervous system • Structural and functional center of the entire nervous system • Consists of the brain and spinal cord • Integrates incoming information from the senses, evaluates the information, and initiates an outgoing response
  4. 4. Peripheral nervous system • Consists of the nerve tissues that lie on the periphery or regions outside the CNS • Cranial nerves – nerves that originate from the brain (or through the skull) • Spinal nerves – nerves that originate from the spinal cord
  5. 5. A-fferent division – consists of all incoming sensory or afferent pathways E-fferent division – consists of all outgoing motor or efferent pathways
  6. 6. Somatic nervous system – carry information to the somatic effectors (skeletal muscles) • Somatic motor division – efferent pathways • Somatic sensory division – afferent pathways • Integrating centers – receive the sensory information and generate the efferent response signal
  7. 7. Autonomic nervous system – carry information to the autonomic (visceral) effectors • Sympathetic division – pathways that exit from the middle portions of the spinal cord; involved in preparing the body to deal with immediate threats: the fight-or-flight response • Para-sympathetic division – exit from the brain or lower portions of the spinal cord and coordinate the body’s normal resting activities; “rest-and-repair” division
  8. 8. Neurons consist of a cell body, one or more dendrites, and one axon • Distal ends of dendrites of sensory neurons are called receptors because they receive the stimuli that initiate nerve signals • Axon hillock – tapered portion of the cell body; “decides” whether to send the impulse any farther in the neuron • Axons with larger diameters conduct nervous impulses faster than those with smaller diameters • Synaptic knobs – release neuro-transmitters
  9. 9. Classification of neurons – three distinct structural types of neurons • Multi-polar neurons – have only one axon but several dendrites • Bi-polar neurons – have only one axon and also only one highly branched dendrite • Uni-polar neurons – sensory neurons with a single process extending from the cell body
  10. 10. Classification of neurons – according to the direction in which they conduct impulses • A-fferent (sensory) neurons – transmit nerve impulses to the spinal cord or brain • E-fferent (motor) neurons – transmit nerve impulses away from the brain or spinal cord to or toward muscles or glands • Inter-neurons – conduct impulses from afferent neurons to or toward motor neurons
  11. 11. Reflex arc – automatic signal conduction route to and from the CNS • Most common form of reflex arc is the three- neuron arc; consists of an: Afferent neuron Interneuron Efferent neuron Synapse – junction between the synaptic knobs of one neuron and the dendrites (or cell body) of another neuron
  12. 12. Neur/o-gli/o - al(Neuroglial)– pertaining to the support cells, glial cells, of nerves. Five basic types: • Astro-cytes – largest and most numerous type of glia; help form the blood-brain barrier (BBB) • Microglia – serve a protective function when the brain is under attack by microorganisms • Ependymal cells – produce the fluid that fills the cavities in the brain and spinal cord • Oligo-dendro-cytes – help hold nerve fibers together and also produce the vitally important myelin sheath in CNS • Schwann cells – support nerve fibers in the PNS and sometimes form a myelin sheath around them
  13. 13. Neur/o – al – (Neural) – Pertaining to nerves. Nerves - bundles of peripheral nerve fibers (axons) held together by several layers of connective tissues • Endo-neurium – delicate layer of fibrous connective tissue surrounding each nerve fiber • Peri-neurium – connective tissue layer surrounding each bundle of nerve fibers (fascicles) • Epi-neurium – fibrous coat surrounding numerous fascicles
  14. 14. Tracts – bundles of nerve fibers within the CNS White matter – bundles of myelinated fibers Gray matter – cell bodies and unmyelinated fibers Nucleus – distinct regions of gray matter within the CNS Ganglia – distinct regions of gray matter within the PNS
  15. 15. Mixed nerves – carry both sensory (afferent) and motor (efferent) fibers Sensory nerves – contain mostly afferent fibers Motor nerves – contain mostly efferent fibers Nerve fibers can sometimes be repaired if the damage is not extensive
  16. 16. Nerve impulse – wave of electrical energy that travels along the plasma membrane of the nerve Cell membrane potential – difference in electrical charge across their plasma membranes • Resting membrane potential (RMP) – mechanism that maintains the potential voltage; when the neuron is not in an excited state, we say that the neuron is “at rest”; typically –70 mV • The slight excess of positive ions on the outer surface is produced by ion transport mechanisms and the membrane’s permeability characteristics • The membrane’s selective permeability characteristics help maintain a slight excess of positive ions on the outer surface of the membrane
  17. 17. Synapse – place where signals are transmitted from one neuron, called the pre-synaptic neuron, to another neuron, called the post-synaptic neuron
  18. 18. Types of synapses • Electrical synapse – where two cells are joined end-to-end by gap junctions; as a result, an action potential simply continues along the postsynaptic plasma membrane as if it belonged to the same cell • Chemical synapses – use a chemical neuro-transmitter to send the message to the postsynaptic cell: • Synaptic knob – contains many small sacs (vesicles) filled with neurotransmitter molecules • Synaptic cleft – fluid-filled space (about one millionth of an inch in width) between a synaptic knob and the plasma membrane of a postsynaptic neuron • Post-synaptic neuron – has protein molecules embedded in it, each facing toward the synaptic knob and its vesicles
  19. 19. Neuro-transmitters – means by which neurons “talk” to one another; more than 50 compounds are now known to be neurotransmitters Neuro-transmitters are commonly classified by their function or by their chemical structure • Excitatory neurotransmitters • Inhibitory neurotransmitters
  20. 20. •Excitation – occurs when a stimulus triggers the opening of stimulus-gated Na+ channels •Inhibition – stimulus triggers the opening of stimulus-gated K+ channels
  21. 21. Action potential – an electrical signal that travels along the surface of a neuron’s plasma membrane • When an adequate stimulus is applied to a neuron, the Na+ channels open at the point of stimulation. Na+ diffuses rapidly into the cell at the site of this local depolarization • If the magnitude of the local depolarization exceeds a limit called the threshold potential (about –59 mV), then additional Na+ channels are opened • As more Na+ rushes into the cell, the membrane moves rapidly toward 0 mV and then continues in a positive direction to a peak of +30 mV • The action potential is an all-or-none response • Once the peak of the action potential is reached, the membrane potential begins to move back toward the resting potential of –70 mV in a process called repolarization • Because the K+ channels often remain open as the membrane reaches its resting potential, too much K+ may rush out of the cell; hyperpolarization
  22. 22. Absolute refractory period – very brief period when a local area of an axon’s membrane resists restimulation
  23. 23. Conduction of the action potential • The action potential never moves backward, restimulating the region from which it just came • In myelinated fibers, the insulating properties of the thick myelin sheath resist ion movement and the resulting flow of current • The rate at which a nerve fiber conducts an impulse depends on its diameter and also on the presence or absence of a myelin sheath
  24. 24. Severe psychic depression occurs when a deficit of norepinephrine, dopamine, serotonin, and other amines exists in certain brain synapses • Anti-depressant drugs – some of these inactivate dopamine and serotonin; others called SSRIs (serotonin-specific reuptake inhibitors) produce antidepressant effects by inhibiting the uptake of serotonin
  25. 25. Cocaine – produces a temporary feeling of well-being in cocaine abusers by blocking the uptake of dopamine Anesthetics – produce their effects by inhibiting the opening of sodium channels in the nerve cell membrane, thus blocking the initiation and conduction of nerve impulses

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